Some computing devices comprises multiple caching agents such as processors and/or I/O hubs. The caching agents may comprise internal caches and/or associated external caches that maintain local copies of data stored in system memory of the computing device. These local copies of data are often referred to as cache lines, memory lines, and/or lines and may comprise 64, 128, 256 or some other number of bytes of data. These computing devices further implement some sort of cache coherency protocol which ensures that cache lines remain coherent with one another and the memory.